Sound treatment

Acoustic sterilisation of medical instruments could help prevent transmission of deadly variant Creutzfeldt-Jakob disease during surgery, US researchers claim.

Prions, proteins that can cause vCJD in humans may contaminate equipment during surgery and examinations and are hard to destroy.

However, a team from the Georgia Institute of Technology and Georgia State University, together with dentist Dr. Stephen Carter, say their ultrasonic wave technique could damage prions and prevent them causing infection.

‘I believe the system would interrupt the transmission of any bacteria or virus,’ said Carter. ‘It should also have an effect on prions by destroying their morphological integrity and preventing them from functioning normally.’

‘Two types of bacteria were chosen as they were good marker organisms,’ said Georgia Institute’s Prof Kenneth Cunefare. ‘They are very common, but have spores that are hard to kill in the dormant stage. But we were able to do this.’

The process allows delicate instruments to be sterilised without using high temperatures or harsh chemicals, and in a fraction of the current time, using a phenomenon known as cavitation.

As sound is applied to a liquid, bubbles are created, releasing energy as they collapse.

Items were placed in a mild solution of isopropyl alcohol at a pressure of two atmospheres, to make the effect more violent, and short bursts of ultrasonic sound were fired through this from a piezo-ceramic cylinder.

The process thinned or ruptured the walls of the bacteria destroying them and allowing the alcohol disinfectant inside to ensure eradication.

Fears of prion transmission caused single use surgical instruments to be introduced to UK hospitals in January 2001 following concerns over the difficulty of sterilising forceps used to remove tonsils and adenoids. By the end of the year re-useable instruments were reintroduced following problems and fatalities blamed on the disposable equipment.

At present surgical instruments such as endoscopes, fibreoptic tubes used to view inside a patient’s throat and digestive system cannot be heat sterilised like other re-useable items as high temperatures damage them.

Instead, they are soaked in baths of hazardous chemicals, meaning they are out of action for a relatively long period.

But last August, 71 Canadians were advised that they might be at risk of contracting vCJD after being examined with an endoscope used on a man who died from the disease.

Researchers say the process could also be used to kill organisms in sewage and water pipelines by placing transducers along them, once the optimum sound levels and hydrostatic pressure for this have been determined.

‘Sound could also be used to kill organisms in milk and orange juice without changing their flavour,’ said Cunefare. ‘This change is a side- effect of pasteurisation techniques using heat.’

The team now plans to improve the technique to treat larger volumes of liquid, and is working on a commercial version of the device.

But UK expert Prof Bill Keevil of Southampton University’s School of Biomedical Sciences urged caution. ‘Two years ago, a Swiss team used ultrasound to break down clumps of rogue prions into smaller units,’ he said. ‘These acted as a template to change other normal prions, which in effect helped the rogue ones to spread.’While the technique may burst the lipid membranes of viruses and bacteria, unless it can be definitely proven that the technique breaks prions down completely, I would be concerned.’